MicroRNA-22 promotes cell survival upon UV radiation by repressing PTEN

DNA damage response upon UV radiation involves a complex network of cellular events required for maintaining the homeostasis and restoring genomic stability of the cells. As a new class of players involved in DNA damage response, the regulation and function of microRNAs in response to UV remain poorly understood. Here we show that UV radiation induces a significant increase of miR-22 expression, which appears to be dependent on the activation of DNA damage responding kinase ATM (ataxia telangiectasia mutated). Increased miR-22 expression may result from enhanced miR-22 maturation in cells exposed to UV. We further found that tumor suppressor gene phosphatase and tensin homolog (PTEN) expression was inversely correlated with miR-22 induction and UV-induced PTEN repression was attenuated by overexpression of a miR-22 inhibitor. Moreover, increased miR-22 expression significantly inhibited the activation of caspase signaling cascade, leading to enhanced cell survival upon UV radiation. Collectively, these results indicate that miR-22 is an important player in the cellular stress response upon UV radiation, which may promote cell survival via the repression of PTEN expression.     

Endoplasmic reticulum stress controls M2 macrophage differentiation and foam cell formation

Macrophages are essential in atherosclerosis progression, but regulation of the M1 versus M2 phenotype and their role in cholesterol deposition are unclear. We demonstrate that endoplasmic reticulum (ER) stress is a key regulator of macrophage differentiation and cholesterol deposition. Macrophages from diabetic patients were classically or alternatively stimulated and then exposed to oxidized LDL. Alternative stimulation into M2 macrophages lead to increased foam cell formation by inducing scavenger receptor CD36 and SR-A1 expression. ER stress induced by alternative stimulation was necessary to generate the M2 phenotype through JNK activation and increased PPARγ expression. The absence of CD36 or SR-A1 signaling independently of modified cholesterol uptake decreased ER stress and prevented the M2 differentiation typically induced by alternative stimulation. Moreover, suppression of ER stress shifted differentiated M2 macrophages toward an M1 phenotype and subsequently suppressed foam cell formation by increasing HDL- and apoA-1-induced cholesterol efflux indicating suppression of macrophage ER stress as a potential therapy for atherosclerosis.     

Eckol isolated from Ecklonia cava attenuates oxidative stress induced cell damage in lung fibroblast cells

We have investigated the cytoprotective effect of eckol, which was isolated from Ecklonia cava, against oxidative stress induced cell damage in Chinese hamster lung fibroblast (V79-4) cells. Eckol was found to scavenge 1,1-diphenyl-2-picrylhydrazyl radical, hydrogen peroxide (H(2)O(2)), hydroxy radical, intracellular reactive oxygen species (ROS), and thus prevented lipid peroxidation. As a result, eckol reduced H(2)O(2) induced cell death in V79-4 cells. In addition, eckol inhibited cell damage induced by serum starvation and radiation by scavenging ROS. Eckol was found to increase the activity of catalase and its protein expression. Further, molecular mechanistic study revealed that eckol increased phosphorylation of extracellular signal-regulated kinase and activity of nuclear factor kappa B. Taken together, the results suggest that eckol protects V79-4 cells against oxidative damage by enhancing the cellular antioxidant activity and modulating cellular signal pathway.     

Ionizing radiation induces mitochondrial reactive oxygen species production accompanied by upregulation of mitochondrial electron transport chain function and mitochondrial content under control of the cell cycle checkpoint

Whereas ionizing radiation (Ir) instantaneously causes the formation of water radiolysis products that contain some reactive oxygen species (ROS), ROS are also suggested to be released from biological sources in irradiated cells. It is now becoming clear that these ROS generated secondarily after Ir have a variety of biological roles. Although mitochondria are assumed to be responsible for this Ir-induced ROS production, it remains to be elucidated how Ir triggers it. Therefore, we conducted this study to decipher the mechanism of Ir-induced mitochondrial ROS production. In human lung carcinoma A549 cells, Ir (10 Gy of X-rays) induced a time-dependent increase in the mitochondrial ROS level. Ir also increased mitochondrial membrane potential, mitochondrial respiration, and mitochondrial ATP production, suggesting upregulation of the mitochondrial electron transport chain (ETC) function after Ir. Although we found that Ir slightly enhanced mitochondrial ETC complex II activity, the complex II inhibitor 3-nitropropionic acid failed to reduce Ir-induced mitochondrial ROS production. Meanwhile, we observed that the mitochondrial mass and mitochondrial DNA level were upregulated after Ir, indicating that Ir increased the mitochondrial content of the cell. Because irradiated cells are known to undergo cell cycle arrest under control of the checkpoint mechanisms, we examined the relationships between cell cycle and mitochondrial content and cellular oxidative stress level. We found that the cells in the G2/M phase had a higher mitochondrial content and cellular oxidative stress level than cells in the G1 or S phase, regardless of whether the cells were irradiated. We also found that Ir-induced accumulation of the cells in the G2/M phase led to an increase in cells with a high mitochondrial content and cellular oxidative stress level. This suggested that Ir upregulated mitochondrial ETC function and mitochondrial content, resulting in mitochondrial ROS production, and that Ir-induced G2/M arrest contributed to the increase in the mitochondrial ROS level by accumulating cells in the G2/M phase.     

Nek10 mediates G2/M cell cycle arrest and MEK autoactivation in response to UV irradiation

Appropriate cell cycle checkpoint control is essential for the maintenance of cell and organismal homeostasis. Members of the Nek (NIMA-related kinase) family of serine/threonine protein kinases have been implicated in the regulation of various aspects of the cell cycle. We explored the cellular functions of Nek10, a novel member of the Nek family, and demonstrate a role for Nek10 in the cellular UV response. Nek10 was required for the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling upon UV irradiation but not in response to mitogens, such as epidermal growth factor stimulation. Nek10 physically associated with Raf-1 and MEK1 in a Raf-1-dependent manner, and the formation of this complex was necessary for Nek10-mediated MEK1 activation. Nek10 did not affect the kinase activity of Raf-1 but instead promoted the autophosphorylation-dependent activation of MEK1. The appropriate maintenance of the G(2)/M checkpoint following UV irradiation required Nek10 expression and ERK1/2 activation. Taken together, our results uncover a role for Nek10 in the cellular response to UV irradiation.     

Genome scale portrait of cAMP-receptor protein (CRP) regulons in mycobacteria points to their role in pathogenesis

cAMP Receptor Protein (CRP)/Fumarate Nitrate Reductase Regulator (FNR) family proteins are ubiquitous regulators of cell stress in eubacteria. These proteins are commonly associated with maintenance of intracellular oxygen levels, redox-state, oxidative and nitrosative stresses, and extreme temperature conditions by regulating expression of target genes that contain regulatory cognate DNA elements. We describe the use of informatics enabled comparative genomics to identify novel genes under the control of CRP regulator in Mycobacterium tuberculosis (M.tb). An inventory of CRP regulated genes and their operon context in important mycobacterial species such as M. leprae, M. avium subsp. paratuberculosis and M. smegmatis and several common genes within this genus including the important cellular functions, mainly, cell-wall biogenesis, cAMP signaling and metabolism associated with such regulons were identified. Our results provide a possible theoretical framework for better understanding of the stress response in mycobacteria. The conservation of the CRP regulated genes in pathogenic mycobacteria, as opposed to non-pathogenic ones, highlights the importance of CRP-regulated genes in pathogenesis.     

UVA influenced the SIRT1‐miR‐27a‐5p‐SMAD2‐MMP1/COL1/BCL2 axis in human skin primary fibroblasts

Both SIRT1 and UVA radiation are involved in cellular damage processes such as apoptosis, senescence and ageing. MicroRNAs (miRNAs) have been reported to be closely related to UV radiation, as well as to SIRT1. In this study, we investigated the connections among SIRT1, UVA and miRNA in human skin primary fibroblasts. Our results showed that UVA altered the protein level of SIRT1 in a time point–dependent manner. Using miRNA microarray, bioinformatics analysis, we found that knocking down SIRT1 could cause up‐regulation of miR‐27a‐5p and the latter could down‐regulate SMAD2, and these results were verified by qRT‐PCR or Western blot. Furthermore, UVA radiation (5 J/cm²), knocking down SIRT1 or overexpression of miR‐27a‐5p led to increased expression of MMP1, and decreased expressions of COL1 and BCL2. We also found additive impacts on MMP1, COL1 and BCL2 under the combination of UVA radiation + Sirtinol (SIRT1 inhibitor), or UVA radiation + miR‐27a‐5p mimic. SIRT1 activator resveratrol could reverse damage changes caused by UVA radiation. Besides, absent of SIRT1 or overexpression of miR‐27a‐5p increased cell apoptosis and induced cell arrest in G2/M phase. Taken together, these results demonstrated that UVA could influence a novel SIRT1‐miR‐27a‐5p‐SMAD2‐MMP1/COL1/BCL2 axis in skin primary fibroblasts, and may provide potential therapeutic targets for UVA‐induced skin damage.     

TGF-β Targets the Wnt Pathway Components,APC and β-catenin,as Mv1Lu Cells Undergo Cell Cycle Arrest

Mammalian cells exhibit complex cellular responses to DNA damage, including cell cycle arrest, DNA repair and apoptosis. Defects in any one of these responses can result in carcinogenesis. Absence of the chromatin remodeling complex Swi/Snf is found in many instances of cancer, and we have investigated its role in the UV damage response. The human carcinoma cell line SW13 is deficient in Swi/Snf and is very sensitive to UV radiation. In contrast, SW13 cells with ectopic Brg1 expression regain active Swi/Snf and become significantly more resistant to UV radiation. Sensitivity to UV light correlates well with dramatic UV induced apoptosis in SW13 cells, but not in SW13 cells expressing Brg1. We show that SW13 cells synchronized at the G1/S border progress into S phase after UV irradiation, and this checkpoint deficiency is corrected after Brg1 expression is restored. Interestingly, Brg1 expression in SW13 cells restores expression of two DNA damage responsive genes, Gadd45a and p21. Furthermore, Gadd45a induction and p21 degradation were observed in the Brg1-expressing SW13 cells after UV irradiation. Our findings demonstrate that Swi/Snf protects cells against deleterious consequences of UV induced DNA damage. These results also indicate that Swi/Snf may play a role in replication checkpoint activation after UV damage via regulation of the two PCNA-binding proteins Gadd45a and p21.